Add --enable-internal-media-session to trigger the MediaSession backend.

content/test/BUILD.gn

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/chrome_build.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
@@ skipping 633 matching lines @@
     "../browser/media/encrypted_media_browsertest.cc",
     "../browser/media/media_browsertest.cc",
     "../browser/media/media_browsertest.h",
     "../browser/media/media_canplaytype_browsertest.cc",
     "../browser/media/media_capabilities_browsertest.cc",
     "../browser/media/media_color_browsertest.cc",
     "../browser/media/media_redirect_browsertest.cc",
     "../browser/media/media_source_browsertest.cc",
     "../browser/media/midi_browsertest.cc",
     "../browser/media/session/audio_focus_delegate_default_browsertest.cc",
+    "../browser/media/session/media_session_browsertest.cc",
     "../browser/media/session/media_session_impl_browsertest.cc",
     "../browser/media/session/media_session_impl_visibility_browsertest.cc",
     "../browser/media/session/media_session_service_impl_browsertest.cc",
     "../browser/media/session/mock_media_session_player_observer.cc",
     "../browser/media/session/mock_media_session_player_observer.h",
     "../browser/memory/memory_coordinator_impl_browsertest.cc",
     "../browser/memory/memory_pressure_controller_impl_browsertest.cc",
     "../browser/message_port_provider_browsertest.cc",
     "../browser/mojo_sandbox_browsertest.cc",
     "../browser/net_info_browsertest.cc",
@@ skipping 1172 matching lines @@
   if (is_android) {
     deps += [ "//testing/android/native_test:native_test_native_code" ]
   }
 }
 
 group("fuzzers") {
   deps = [
     "//content/test/fuzzer",
   ]
 }